VALHALLA, N.Y. (CBSNewYork) — Bacterial contamination was being blamed Monday for an outbreak of foodborne illness following the popular Burger & Beer Bash in Westchester County earlier this month.

The county Health Department said Monday that the campylobacter bacterium was to blame for the outbreak at the June 6 outdoor food festival at the Kenisco Dam in Valhalla.

The bacterium was identified through tests on samples from several people who got sick at the event. The department did not specify exactly how many people were sickened.

But health officials have not determined the source of the bacteria, since most attendees ate food from many of the 30 different vendors at the event, the department said. The department has launched an investigation and has been interviewing people in an effort to trace the source.

For most people sickened by the campylobacter outbreak, the illness will resolve without medication within three to five days – although it could be up to 10 days, the department said. In cases where a person’s immune system is weakened by illness or medication, or in especially severe cases, antibiotics may be prescribed, the department said.

A campylobacter infection can cause diarrhea, vomiting and fever, the department said.

“Anyone who has not already become sick following this event should no longer be at risk,” Westchester County Health Commissioner Dr. Sherlita Amler said in a news release. “Anyone who continues to have symptoms should contact his or her physician and should not go to work or school until symptoms resolve.”

The Westchester County Health Department issues more than 500 temporary food service permits annually, and a disease outbreak has not occurred in some time, the department said.

“As part of our response, the health department will send sanitarians to each of the food service establishments who participated in the festival to provide a refresher to restaurant staff about food safety, with special emphasis on safe off-site practices,” Amler said in the release. “Sanitarians will also conduct a detailed food preparation review by observing as restaurant staffers prepare the foods they served at the June 6 event.”

Most cases of campylobacter infection are the result of eating raw or undercooked meat, or cross-contaminated food. Symptoms usually come on within two to five days of infection.